Power Allocation Effect on Capacity of Single Carrier Power Domain Non-Orthogonal Multiple Access (NOMA)

Non-Orthogonal Multiple Access (NOMA) has become one of the most discussed topics nowadays in the mobile cellular world. Plenty of papers say the NOMA system is superior to the previous technology used in fourth-generation (4G) and due to its high spectral efficiency makes it a promising candidate for the fifth generation (5G) mobile communication system. However, NOMA is simulated with only two or three users in a single carrier in most of those works, making readers wonder how many users it can support. In this paper, the NOMA system with a hundred users is simulated to see each sum capacity or spectral efficiency in bit per second per Hz. Both fixed power allocation and dynamic power allocation methods are used in order to compare the performance. Channel State Information (CSI) based power allocation method, which is the dynamic power allocation, outperforms the Fixed Power Allocation (FPA) method. The resulting graphic shows that FPA increases sum capacity to one peak point but decreases as more users are added. On the other hand, CSIbased power allocation significantly increases the sum capacity to one point and then remains stable as the number of users is added.